Retrieval Device, Retrieval System, Retrieval Method, Retrieval Program, and Computer-Readable Recording Medium Storing Retrieval Program

1. A retrieval device comprising: an extraction unit for referring to a comment storage unit for storing comment data indicating a comment on an item by a user and extracting comment data indicating a second comment containing a uniform resource locator (URL) link to a first comment, the first comment being a comment on a first item by a first user and the second comment being a comment on a second item by a second user; an association unit for generating associated item data indicating that the first and second items are associated with each other based on that the second comment indicated by the second comment data extracted by the extraction unit contains the URL link to the first comment, and storing the associated item data into an associated item storage unit; a receiving unit for receiving a request for information about one item of the first and second items from a user terminal; a retrieval unit for referring to an item storage unit for storing item information and extracting designated item information about the one item corresponding to the request received by the receiving unit, and referring to the item storage unit and the associated item storage unit and extracting associated item information about another item of the first and second items; and a transmitting unit for transmitting the designated item information and the associated item information extracted by the retrieval unit to the user terminal, wherein the association unit determines whether a specified word is included in the second comment indicated by the extracted comment data and, when the specified word is included, adds a higher score to the associated item data than when not, wherein, when a plurality of associated item information are extracted, the retrieval unit sorts the plurality of associated item information so that the associated item information with the higher score is displayed preferentially on the user terminal, and wherein the specified word is a word from which it can be estimated that the second comment is made on the first item indicated by the first comment already made by the first user.

2. The retrieval device according to claim 1 , wherein the association unit determines whether categories of the first and second items are common by referring to the item storage unit and, when the categories are common, adds a higher score to the associated item data than when not, and when a plurality of associated item information are extracted, the retrieval unit sorts the plurality of associated item information so that the associated item information with the higher score is displayed preferentially on the user terminal.

3. The retrieval device according to claim 1 , wherein the association unit refers to a user storage unit for storing user information and adds a user attribute common to the first and second users to the associated item data, and the retrieval unit extracts the user information about a user of the user terminal from the user storage unit and, when a user attribute indicated by the user information corresponds to the common user attribute added to the extracted associated item information, determines to transmit the associated item information to the user terminal and, when not, determines not to transmit the associated item information to the user terminal.

4. The retrieval device according to claim 1 , wherein when the first comment cannot be uniquely specified from the link contained in the second comment, the extraction unit determines that the link is a link to a comment by the first user when a difference between created time of the comment by the first user and created time of the second comment is equal to or less than a specified threshold, and the association unit generates the associated item data, treating an item on which the comment by the first user determined to be a linked comment is made as the first item.

5. A retrieval system comprising: an extraction unit for referring to a comment storage unit for storing comment data indicating a comment on an item by a user and extracting comment data indicating a second comment containing a uniform resource locator (URL) link to a first comment, the first comment being a comment on a first item by a first user and the second comment being a comment on a second item by a second user; an association unit for generating associated item data indicating that the first and second items are associated with each other based on that the second comment indicated by the second comment data extracted by the extraction unit contains the URL link to the first comment, and storing the associated item data into an associated item storage unit; a receiving unit for receiving a request for information about one item of the first and second items from a user terminal; a retrieval unit for referring to an item storage unit for storing item information and extracting designated item information about the one item corresponding to the request received by the receiving unit, and referring to the item storage unit and the associated item storage unit and extracting associated item information about another item of the first and second items; and a transmitting unit for transmitting the designated item information and the associated item information extracted by the retrieval unit to the user terminal, wherein the association unit determines whether a specified word is included in the second comment indicated by the extracted comment data and, when the specified word is included, adds a higher score to the associated item data than when not, wherein, when a plurality of associated item information are extracted, the retrieval unit sorts the plurality of associated item information so that the associated item information with the higher score is displayed preferentially on the user terminal, and wherein the specified word is a word from which it can be estimated that the second comment is made on the first item indicated by the first comment already made by the first user.

6. A retrieval method executed by a computer, comprising: an extraction step of referring to a comment storage unit for storing comment data indicating a comment on an item by a user and extracting comment data indicating a second comment containing a uniform resource locator (URL) link to a first comment, the first comment being a comment on a first item by a first user and the second comment being a comment on a second item by a second user; an association step of generating associated item data indicating that the first and second items are associated with each other based on that the second comment indicated by the second comment data extracted in the extraction step contains the URL link to the first comment, and storing the associated item data into an associated item storage unit; a receiving step of receiving a request for information about one item of the first and second items from a user terminal; a retrieval step of referring to an item storage unit for storing item information and extracting designated item information about the one item corresponding to the request received in the receiving step, and referring to the item storage unit and the associated item storage unit and extracting associated item information about another item of the first and second items; and a transmitting step of transmitting the designated item information and the associated item information extracted in the retrieval step to the user terminal, wherein the association step comprises determining whether a specified word is included in the second comment indicated by the extracted comment data and, when the specified word is included, adding a higher score to the associated item data than when not, wherein the retrieval step comprises, when a plurality of associated item information are extracted, sorting the plurality of associated item information so that the associated item information with the higher score is displayed preferentially on the user terminal, and wherein the specified word is a word from which it can be estimated that the second comment is made on the first item indicated by the first comment already made by the first user.

7. A non-transitory computer-readable recording medium storing a retrieval program causing a computer to function as: an extraction unit for referring to a comment storage unit for storing comment data indicating a comment on an item by a user and extracting comment data indicating a second comment containing a uniform resource locator (URL) link to a first comment, the first comment being a comment on a first item by a first user and the second comment being a comment on a second item by a second user; an association unit for generating associated item data indicating that the first and second items are associated with each other based on that the second comment indicated by the second comment data extracted by the extraction unit contains the URL link to the first comment, and storing the associated item data into an associated item storage unit; a receiving unit for receiving a request for information about one item of the first and second items from a user terminal; a retrieval unit for referring to an item storage unit for storing item information and extracting designated item information about the one item corresponding to the request received by the receiving unit, and referring to the item storage unit and the associated item storage unit and extracting associated item information about another item of the first and second items; and a transmitting unit for transmitting the designated item information and the associated item information extracted by the retrieval unit to the user terminal, wherein the association unit determines whether a specified word is included in the second comment indicated by the extracted comment data and, when the specified word is included, adds a higher score to the associated item data than when not, wherein, when a plurality of associated item information are extracted, the retrieval unit sorts the plurality of associated item information so that the associated item information with the higher score is displayed preferentially on the user terminal, and wherein the specified word is a word from which it can be estimated that the second comment is made on the first item indicated by the first comment already made by the first user.